Ripening and quality of ‘Laetitia’ plums following harvest and cold storage as affected by inhibition of ethylene action (1)

Ripening and quality of ‘Laetitia’ plums following harvest and cold storage

as affected by inhibition of ethylene action

Luiz Carlos Argenta(2)_{, Juliana Golin Krammes}(2)_{, Clarice Aparecida Megguer}(2) _,

Cassandro Vidal Talamini Amarante(3) _{and James Mattheis}(4)

Abstract – The inhibition of ethylene action by 1-methylcyclopropene (1-MCP) extends shelf and storage life of many climacteric fruits. However, 1-MCP appears to have limited effects on stone fruit depending on specie and cultivar. The effects of 1-MCP on ripening and quality of ‘Laetitia’ plums were determined during ripening at 23o_{C following harvest and cold storage. Japanese plums (Prunus salicina,cv. Laetitia)} were harvested at mature pre-climacteric stage,cooled to 2o_{C within 36 hours of harvest and then treated} with 0, 0.05, 0.10, 0.50 or 1.00 µL L-1 _{of 1-MCP at 1°C for 24 hours. Following treatment, fruits were} either held at 23o_{C for 16 days or stored at 1}o_{C for 50 days. Fruits were removed from cold storage at} 10-day intervals and allowed to ripe at 23°C for five days. A delay of climacteric respiration and ethylene production by 1-MCP treatment during ripening following harvest and cold storage was associated to a slow rate of fruit softening. 1-MCP treatment also delayed the loss of titratable acidity and changes of flesh and skin color, whereas it had little or no effect on soluble solids content. 1-MCP effects were concentration-and storage duration-dependent concentration-and, generally, a saturation fruit response to 1-MCP occurred between 0.5 and 1.0 µL L-1_{. During ripening, 1-MCP treated fruits attained quality similar to that of controls. Results} indicated that 1-MCP treatment may extend shelf life (23o_{C) and storage life (1}o_{C) of ‘Laetitia’plums by} approximately six and 20 days, respectively.

Index terms: Prunus salicina, fruit pulps, firmness, shelf life, fruit, colour.

Efeitos da inibição da ação do etileno na maturação e qualidade de ameixas ‘Laetitia’ após a colheita e armazenagem refrigerada

Resumo – A inibição da ação do etileno pelo 1-metilciclopropeno (1-MCP) prolonga a vida de prateleira e de armazenagem de vários frutos climatérios. Entretanto, 1-MCP parece ter efeitos limitados em frutas de caroço dependendo da espécie e cultivar. Os efeitos do 1-MCP na maturação e qualidade de ameixas ‘Laetitia’ foram determinados durante a maturação a 23o_{C após a colheita e após a armazenagem refrigerada.} Ameixas (Prunus salicina,cv. Laetitia) foram colhidas em estádio pré-climatério, resfriadas a 2o_{C em} 36 horas da colheita e então tratadas com 1-MCP nas doses de 0; 0,05; 0,10; 0,50 ou 1,00 µL L-1 _{a 1°C} por 24 horas. Após o tratamento os frutos foram mantidos a 23o_{C por 16 dias ou armazenados a 1}o_{C por} 50 dias. Os frutos foram removidos da câmara de armazenagem refrigerada a cada 10 dias e então deixados a amadurecer a 23°C, por cinco dias. O retardamento do climatério respiratório e da produção de etileno pelo tratamento 1-MCP durante a maturação após a colheita e após a armazenagem refrigerada foi associado à redução da taxa de amolecimento da polpa dos frutos. O tratamento 1-MCP também retardou a perda da acidez titulável e as mudanças de coloração da polpa e da epiderme, mas teve pequeno ou nenhum efeito sobre o teor de açúcares solúveis. Os efeitos do 1-MCP dependeram da sua concentração e do período de armazenagem dos frutos e, normalmente, a dose de saturação das respostas dos frutos ao 1-MCP ocorreu entre 0,5 e 1,0 µL L-1_{. Durante a maturação, ameixas tratadas com 1-MCP desenvolveram qualidade} semelhante a dos frutos controle. Os resultados indicam que o tratamento 1-MCP pode estender a vida de prateleira (23o_{C) e de armazenagem (1}o_{C) de ameixas ‘Laetitia’ por aproximadamente seis e 20 dias,} respectivamente.

Termos para indexação: Prunus salicina, polpa de fruta, firmeza, prazo de validade, fruto, cor.

(1)_{Accepted for publication on August 18, 2003.}

(2)_{Empresa de Pesquisa Agropecuária e Extensão Rural de Santa}

Catarina, Estação Experimental de Caçador, Caixa Postal 591, CEP 89500-000 Caçador, SC. E-mail: argenta@epagri.rct-sc.br, ju.golin@bol.com.br, cmegguer@hotmail.com

(3)_{Universidade do Estado de Santa Catarina, Centro de Ciências}

Agroveterinárias, Caixa Postal 281, CEP 88502-970 La-ges, SC. E-mail: amarante@cav.udesc.br

(4)_{United States Department of Agriculture, Tree Fruit Research}

Introduction

Most fresh plums marketed in Brazil are imported

because local production is greatly limited by orchard

diseases (Ducroquet & Mondin, 1997; Ducroquet

et al., 2001). Despite this constraint, profitable

commercial orchards have been established in

Southern Brazil after the introduction of new plum

cultivars and integrated methods to prevent the main

tree diseases (Ducroquet & Mondin, 1997). As the

plum production increases, new technologies for

postharvest maintenance of fruit quality are required.

Laetitia (FFTRI, South Africa) is a Japanese plum

cultivar fairly adapted to the Southern Brazilian

climate, resistant to

Xantomonas

spot and moderately

tolerant to leaf scald (Ducroquet et al., 2001).

Improving postharvest life would increase the

marketing period of this late season cultivar.

Plums have a short postharvest life compared to

other climacteric temperate fruits such as apples and

pears (Kader, 1992). Low temperature is the most

effective mean to delay postharvest ripening and

deterioration of plums and to schedule ripening

according to marketing needs (Kader & Mitchell,

1989; Mitchell & Kader, 1989a). However, many plum

cultivars, such as Laetitia, might develop chilling

injury, depending on storage temperature and span

(Mitchell & Kader, 1989a; Taylor 1996; Abdi et al.,

1997a).

Cold storage, under modified atmosphere (Couey,

1965; Crouch, 1998) and controlled atmosphere (CA)

(Mitchell & Kader, 1989b; Truter & Combrink, 1997)

improves flesh firmness and ground color retention

and reduces shrivel in some plum cultivars. However,

CA does not prevent chilling injury and may reduce

the flavor after long-term storage, limiting its

commercial use to extend plums storage life (Eksteen

et al., 1986; Mitchell & Kader, 1989b; Truter &

Combrink, 1997).

Removal of ethylene from the environment

surrounding stone fruits might improve storage,

because ripening is regulated by ethylene (Kader &

Mitchell, 1989). However, most methods to remove

ethylene from commercial storage rooms have normally

been ineffective since many fruits are harvested in

advanced ripening stage, when endogenous ethylene

reaches 1 to 3

µ

L L

_{that is high enough to trigger stone}

fruit ripening (Mitchell & Kader, 1989a).

Inhibition of ethylene action by

1-methylcyclopropene (1-MCP) (Sisler & Serek,

1997) effectively delays ripening and extends

postharvest life of climacteric fruits such as banana,

apple, and tomato (Blankenship & Dole, 2003). The

use of 1-MCP also reduces ethylene production and

improves quality of stone fruits such as plum,

apricot, nectarine, and peach during shelf life (Abdi

et al., 1998; Fan et al., 2000; Dong et al., 2001a; Fan

et al., 2002). However, 1-MCP may have different

effects on ripening and quality attributes of stone

fruits after cold storage. Treatment with 1-MCP at

harvest extends cold storage life of plum (Dong et al.,

2002) and apricot, cultivar Perfection (Fan et al.,

2000), whereas it can increase chilling injury in some

cultivars of nectarine (Dong et al., 2001a), apricot

(Dong et al., 2002) and peach (Fan et al., 2002) after

long-term cold storage.

The objective of this work was to determine the

effects of 1-MCP on ripening and quality attributes

of ‘Laetitia’ plum at room temperature following

harvest and cold storage.

Material and Methods

Fruit, 1-MCP treatment, ripening, and storage

conditions

‘Laetitia’ plums (Prunus salicina) of uniform size

(102±4 g) were harvested from an experimental orchard in Central Santa Catarina State at mature pre-climacteric stage on February 2002. The fruits were harvested from selected 7 to 8 year-old trees of ‘Laetitia’ plums grafted on peach seedlings rootstock. The fruits werecooled to 2o_C

within 36 hours of harvest and then treated with 0, 0.05, 0.10, 0.50 or 1.00 µL L-1 _{of 1-MCP (1-methylcyclopropene)}

at 1°C for 24 hours in a 340 L container (made of PVC, with a plastic glass lid and a sealing rubber belt). The 1-MCP was generated as a gas outside the treatment container by mixing SmartFreshTM _{powder (AgroFresh Inc., 0.14% a.i.)}

and water in a 500 mL flask at 35o_{C. The 1-MCP gas was}

pumped from the flask into the container for 10-15 min via a closed loop, as described by Fan et al. (2002). Following treatment, fruits were placed on plastic trays and either maintained at 23o_{C (75±8% RH) for 16 days or}

stored at 1o_{C (80±5% RH) for 20 to 50 days. Fruit samples}

were removed from cold storage at 10-day intervals and allowed to ripe at 23o_{C for five days. During ripening,}

firmness, titratable acidity (TA), soluble solids content (SSC) and fruit color were assayed every four days following harvest, and after five days following cold storage.

Ethylene production, respiration, and 1-MCP

determination.

For ethylene production and respiration analyses, fruits were placed in 4 L glass jars maintained at 23o_{C and supplied}

with compressed ethylene free air, at 100 mL min-1_{. Effluent}

air was analyzed for CO2 and ethylene concentrations by

a gas chromatograph equipped with a methanizer, two flame ionization detectors, a stainless steel column (with 1.0 m and 2.0 mm i.d.) packed with 80 to 100 mesh Poropak Q (for CO2) and a glass column (with 0.6 m and

3.2 mm i.d.) packed with 80 to 100 mesh Poropak Q (for ethylene). Oven, detectors, methanizer and injector temperatures were set at 45, 120, 300 and 110o_C,

respectively.

Headspace concentration of 1-MCP in the treatment containers was measured 10-15 min after fruit treatment started, using the same method used for ethylene analysis, except that 1-MCP gas was used as standard and that the oven temperature was 90o_{C. Gas flows for N}

2, H2 and air

were 70, 30 and 300 mL min-1_{, respectively for all ethylene,}

CO2 and 1-MCP analyses.

Analysis of fruit quality

Firmness was measured on two pared cheek sides of each fruit with a pressure tester fitted with an 8 mm (diameter) probe. Two flesh slices were taken from the opposite sides of each fruit and four slices were combined to prepare a juice sample on a Champion juicer. The SSC (soluble solids content) and TA (titratable acidity) were assayed for each freshly prepared juice sample. The SSC was measured using a digital refractometer and TA was determined by titrating 5 mL of juice with 0.1 N NaOH to pH 8.2 using an autotitrator. Skin and flesh color, measured as hue angle and lightness (L) (Hunter & Harold, 1987), were assayed using a chromameter. Flesh color was measured on the same pared surface used for firmness assessment. Fruits were then cut through equatorial axis and the mesocarp visually assessed for internal disorders and decay as clear (1) or affected (2).

Experimental design and statistical data analysis

The experiment followed a completely randomized design with 21 fruits per treatment and storage duration

combination. There were three replicates of seven fruits for analysis of ethylene production and respiration, 21-fruit replicates for analysis of fruit firmness and color and five replicates of four fruits for analysis of SSC and TA. The data were subjected to analysis of variance using SAS (SAS Institute, Raleigh, USA). The least significant difference (LSD) between treatment means was assessed by Fisher’s least significant difference test (α = 0.05). Unless otherwise mentioned, only the significant (P<0.05) effects of ripening and storage period were discussed.

Results and Discussion

Fruit ripening and quality following harvest

Both CO

and ethylene production by control fruit

increased (P<0.05) from a minimum level to a peak,

then declined during ripening at 23

_{C (Figure 1). The}

1-MCP treatment delayed the rise of both respiration

and ethylene production; ethylene production

increased (P<0.05) from the first to sixth day in control

fruits, from the sixth to ninth in fruit treated with

1-MCP at 0.05

µ

L L

_{and from the eighth to eleventh in}

fruit treated with 1-MCP at 0.5 or 1

µ

L L

_{. The maximum}

rate of ethylene production was not affected by

1-MCP at lowest concentration but it was slightly

reduced by 1-MCP at 0.5 or 1

µ

L L

_.

Maximum respiration rates were detected between

five and seven days ripening in control fruits and

between nine and 13 days ripening in treated fruits

regardless of 1-MCP concentration. Differences in

respiration rates among 1-MCP concentrations were

significant only after six and eight days of ripening,

when fruits treated with the lowest concentration

exhibited higher respiration than fruits treated with

the highest concentration.

Firmness and titratable acidity (TA) decreased

(P<0.05) during fruit ripening (Figure 2). Flesh color

changed from orange to dark-red while skin color

changed from bright red to purple, as indicated by

the reduction of the hue angle and lightness. Fruit

treated with 1-MCP exhibited lower rates of softening,

TA loss and color change relative to untreated fruit

(Figure 2). Plums treated with 0.5 or 1.0

µ

L L

_1-MCP

were 7-10 N firmer and had approximately 34% higher

TA than control fruits between four and 10 days

ripening.

associated with a quick fruit softening during

ripen-ing at 23

_{C following harvest (Figures 1 and 2). This}

ripening behavior is characteristic to most plum

tivars (Kader & Mitchell, 1989). However, other

cul-tivars, termed as suppressed-climacteric (Abdi et al.,

1997b) or very slow-ripening (Crisosto, 1999), exhibit

a maximum ethylene production 15 to 500 fold lower

and a longer shelf life than typical climacteric

culti-vars (Abdi et al., 1997b; 1998). Generally, plums are

highly perishable and, depending on cultivar, may

soften 3.5 to 9.0 N a day at 25°C (Crisosto, 1999). The

delay of climacteric respiration and ethylene

production by 1-MCP treatment leads to a slow rate

of plum softening (Dong et al., 2001b, 2002) (Figures 1

and 2).

Fruit softening is the most sensitive to ethylene

ripening-related process (Lelièvre et al., 1997) and, a

suitable predictor of potential shelf life for plum when

decay and chilling injury are not limiting factors

(Kader & Mitchell, 1989). Plums that reach flesh

firmness of 9 N are considered ripe and ‘ready to eat’

(Crisosto, 1999). The ‘ready to eat’ ripeness was

reached between the 4

_{and 7}

_{day by the control}

and the 10

_{and 13}

_{day by fruit treated with}

1-MCP at 0.50 or 1.00

µ

L L

_{indicating that}

1-MCP treatment may extend shelf life following

harvest (at 23

_{C) of ‘Laetitia’}

_{plum by approximately}

six days (Figure 2).

The 1-MCP effects were concentration-dependent

for firmness and for fruit color after seven and 10 days

and for TA after seven days ripening. Depending on

the storage period, fruits treated with 0.05

µ

L L

1-MCP were softener, less acid and redder than fruits

treated with 0.5 or 1

µ

L L

_{1-MCP. Over the}

ripe-ning period, fruits treated with 1

µ

L L

_{1-MCP had}

similar quality compared to those treated with

0.1 and 0.5

µ

L L

_{1-MCP. The soluble solids content}

(SSC) increased (P<0.05) during the first four days

ripening in controls and during the first four or seven

days of ripening in fruits treated with 1-MCP.

Treatment with 1-MCP only affected SSC after four

days of ripening, however, it reduced (P<0.05) the

SSC/TA ratio for fruits held at 23

_{C following harvest.}

When fruits reached the ‘ready to eat’ firmness,

SSC/TA ratio was 11.8 in the control and 10.9 in fruit

treated with 1-MCP at 0.50 or 1.00

µ

L L

_.

Fruit ripening and quality following cold storage

Respiration and ethylene production by control

and fruit treated with 1-MCP increased (P<0.05)

within five days ripening following cold storage

(Figures 3 and 4). Maximum rates of ethylene and

CO

production at 23

C following cold storage were

treatment and storage duration-dependent. Maximum

rates of ethylene production in control declined

continuously with prolonged storage period and

1-MCP delayed this loss of fruit ability to produce

ethylene during ripening following cold storage

(Figure 3). Maximum ethylene production by fruits

treated with 1-MCP at 0.05 and 0.5

µ

L L

_occurred

following 30 or 40 days (P<0.05) storage. Rates of

ethylene produced by fruits treated with 1-MCP at

0.05 or 0.10

µ

L L

_{were lower than those of the}

control following 20 days of cold storage, but higher

than those of the control following 30-50 days of

Et

hy

len

e (

µ

mo

l k

g

-1 h -1)

0 2 4 6

0 2 4 6 8 10 12 14 16

CO

2

(

mmo

l k

g

-1 h -1)

0.5 1.0 1.5

Days at 23o_{C after treatment}

cold storage (Figure 3). Rates of ethylene produced

by fruits treated with 1-MCP at 0.50 or 1.0

µ

L L

_were

lower than those of the control following 20 and

30 days of cold storage, similar to those of the control

following 40 days of cold storage, and higher than

those of the control following 50 days of cold storage.

Respiration rates on control following 20 and

30 days on storage were similar to or higher than

those on fruit treated with 1-MCP, depending on

ripening period and 1-MCP concentration (Figure 4).

Fi

rm

ne

ss

(N

)

0 10 20 30 40

TA (

%

)

0.5 1.0 1.5

Days at 23o_{C after treatment}

0 4 8 12 16

SSC (

%

)

11 12 13

Ski

n h

ue

0 10 20 30 40

Fl

es

h hue

20 40 60 80

0 4 8 12 16

Fl

es

h L

30 40 50

Figure 2. Changes of firmness, titratable acidity (TA), soluble solids content (SSC), skin and flesh hue, and flesh

Respiration was not affected by 1-MCP treatments

after 40 and 50 days storage regardless of the storage

period. Maximum respiration rates were lower

following 50 days ripening than at an earlier storage

period, regardless of 1-MCP treatment.

Rates of ethylene production by stone fruits

(Wang & Adams, 1982; Brecht & Kader, 1984; Valero

et al., 1997), as well as by apple and pear (Knee et al.,

1983), during ripening at warm temperature can be

stimulated by prior exposure to low temperatures.

However, prolonged storage at low temperatures may

decrease fruit capacity to produce ethylene, which

can be associated to the development of chilling

injury (Wang & Adams, 1982; Brecht & Kader, 1984;

Mollendorff & De Villiers, 1988; Valero et al., 1997;

Fernandez-Trujillo et al., 1998; Dong et al., 2002).

‘Laetitia’ plums might develop chilling injury as a

flesh gel breakdown, when stored at low temperatures

(Truter & Combrink, 1997; Crouch, 1998). However,

no visual symptom of chilling injury on ‘Laetitia’

plums was detected in the present study.

The reduction of fruit ability to produce ethylene

after prolonged cold storage period (Figure 3) might

be attributed to the fruit over-ripen stage, as indicated

by the very low fruit firmness after prolonged storage

period (Figure 5). It has been suggested that the

senescent-promoting action of ethylene, combined

with prior exposure to a chilling temperature, may

damage the enzymatic system that converts ACC to

Figure 3. Ethylene production by ‘Laetitia’ plums treated with 0 ( ), 0.05 ( ), 0.1 ( ), 0.5 ( ) and 1.0 µL L-1 _{( )} 1-methylcyclopropene at harvest, stored for 20-50 days at 1°C and then maintained at 23°C for 5 days. Bars represent LSD0.05 between treatment means.

Et

hyl

ene

(

µ

mo

l k

g

-1h -1)

0 2 4

0 1 2 3 4 5

0 2 4

Days at 23o_{C after storage}

0 2 4

0 1 2 3 4 5

0 2 4

20 days 30 days

ethylene (Brecht & Kader, 1984).

Most of softening, TA losses and changes of flesh

and skin color on control fruit occurred during the

first 10 days storage plus five days ripening

(Figure 5). The 1-MCP delayed these changes in a

concentration-dependent manner. Major effects of

1-MCP were detected at concentrations of 0.5 or

1

µ

L L

_{, after ripening of the 10-30 day-storage}

fruits. Of all fruit color attributes, flesh hue was the

most affected by 1-MCP.

Low temperature storage of ‘Laetitia’ plum delays

beneficially ripening and 1-MCP treatment enhances

low temperature effects on retention of fruit firmness

(Figures 3-5). Flesh firmness of control fruits was 9 N

(‘ready to eat’) after 10 days of storage at 1

_{C plus}

ripening while 1-MCP treated fruits reached 9 N of

firm-ness after 30 days on storage plus ripening (Figure 5).

These results indicate that 1-MCP treatment may

ex-tend storage life (at 1

_{C) of ‘Laetitia’}

_{plum by about}

20

days. Beneficial effects of a single

application of 1-MCP treatment on retention of fruit

firmness have been previously demonstrated for other

stone (Fan et al., 2000, 2002; Dong et al., 2002) and

pome (Blankenship & Dole, 2003) fruits.

SSC and TA are two of the most important quality

indices for stone fruits (Crisosto, 1999). For plum,

1-MCP effects on TA appear to be cultivar and

storage temperature dependent. Loss of TA is slowed

by 1-MCP in typical climacteric plum cultivars, such

as Laetitia (Figures 2 and 5) and Royal Zee (Dong

Figure 4. CO2 production by ‘Laetitia’ plums treated with 0 ( ), 0.05 ( ), 0.1 ( ), 0.5 ( ) and 1.0 µL L-1 ( ) 1-methylcyclopropene at harvest, stored for 20-50 days at 1°C and then maintained at 23°C for 5 days. Bars represent LSD0.05 between treatment means.

CO

2

(m

m

ol

k

g

-1 h

-1 ) _0.5

1.0 1.5 2.0

0 1 2 3 4 5

0.5 1.0 1.5 2.0 0.5 1.0 1.5 2.0

0 1 2 3 4 5

0.5 1.0 1.5 2.0

Days at 23o_{C after storage}

20 days 30 days

et al., 2002), but not in suppressed-climacteric type

of plum, such as Red Rosa (Dong et al., 2001b).

Impact of 1-MCP on retention of TA by ‘Laetitia’ was

more evident during ripening at 23

_{C following}

harvest than after cold storage (Figures 2 and 5). SSC

and SSC/TA ratio were not affected by 1-MCP

treatment in cold stored fruit (Figure 5). Propylene

treatment hastens the reduction of hue values in

plum (Abdi et al., 1998) while 1-MCP treatment delays

(Figures 2 and 5), indicating that color changes during

Figure 5. Changes of firmness, titratable acidity (TA), soluble solids content (SSC), skin and flesh hue, and flesh lightness (L) in ‘Laetitia’ plums treated with 0 ( ), 0.05 ( ), 0.1 ( ), 0.5 ( ) and 1.0 mL L-1 _{( ) 1-methylcyclopropene at harvest,} stored for 20-50 days at 1°C and then maintained at 23°C for 5 days. Bars represent LSD0.05 between treatment means.

Fi

rm

ne

ss

(N

)

0 10 30 40

TA (

%

)

0.5 1.0 1.5

Days in cold storage

0 10 20 30 40 50

SS

C (

%

)

11 12 13

Ski

n hue

0 10 20 30 40

Fl

es

h h

ue

20 40 60 80

0 10 20 30 40 50

Fl

es

h L

plum ripening is an ethylene-dependent process.

However, in suppressed-climacteric types of plum,

1-MCP also delayed hue changes, and fruit attained

full color without development of climacteric ethylene

production

(Abdi et al., 1998). Color changes can be

either ethylene dependent or independent, according

to the type of pigment involved and the fruit species

(Lelièvre et al., 1997). In plums, the main color

changes are based on accumulation of anthocinines

(Wesche-Ebeling et al., 1996).

The 1-MCP effects on ethylene production and

quality were concentration dependent, although there

were little or no significant differences to the increase

of 1-MCP concentration from 0.50 to 1.00

µ

L L

_,

indicating a saturation response to 1-MCP.

Conclusions

1. ‘Laetitia’ plum has a rapid postharvest loss of

fruit quality associated to a climacteric type of

respiration and ethylene production.

2. The 1-MCP treatment delays the increase of

climacteric respiration and ethylene production by

plum during ripening following harvest and cold

storage.

3. A fruit saturation response to 1-MCP occurs at

0.50-1.00

µ

L L

_.

4. The 1-MCP treatment has the potential to

control the ripening and extend shelf and storage life

of plum.

5. The 1-MCP treatment extends shelf life (at 23

_C)

following harvest and storage life (at 1

_{C) of ‘Laetitia’}

plum by approximately six and 20 days, respectively.

Acknowledgement

To Rhom and Haas Company, for financial

support.

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